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Proceedings Paper

High-current-density small-area SIS junctions for high-frequency radio astronomy
Author(s): Eric E. Bloemhof
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Paper Abstract

At the Smithsonian Astrophysical Observatory, we have been developing expertise in the construction of high-frequency heterodyne receivers using SIS junctions as their first mixing elements. This research has been carried out in support of the Submillimeter Array (SMA), a radio interferometer soon to be built on Mauna Kea that will require multiple reciever systems at a number of bands between 177 GHz and 920 GHz. In this paper, we describe research on the fabrication of all-refractory SIS junctions. To be useful as high-frequency mixers, SIS junctions must have small area and high critical current density. At the lower SMA frequencies, Nb/Al-Oxide/Nb ahs proven to be an ideal material system, and optical photolithography has sufficient resolution for junction definition. At the higher frequencies, NbN/MgO/NbN may enjoy an advantage due to its larger energy gap, and electron-beam lithography may be necessary for defining junctions much smaller than one micron in size. We report good initial results for Nb/Al-Oxide/Nb junctions, fabricated using a self-aligned optical technique, with area $AP 0.5 micrometers 2 and critical current density $AP 10,000 Amp/cm2.

Paper Details

Date Published: 2 July 1994
PDF: 11 pages
Proc. SPIE 2160, Superconductive Devices and Circuits, (2 July 1994); doi: 10.1117/12.180990
Show Author Affiliations
Eric E. Bloemhof, Harvard-Smithsonian Ctr. for Astrophysics (United States)

Published in SPIE Proceedings Vol. 2160:
Superconductive Devices and Circuits
Robert A. Buhrman; John T. Clarke; Ken Daly; Roger H. Koch; Jerome A. Luine; Randy W. Simon, Editor(s)

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